1. Field of the Invention
This invention relates to a speed regulator system for a d.c. motor, and more specifically to an impact load controller for use with a speed controller of such a system.
2. Description of the Prior Art
In the threading stage of a hot or cold tandem rolling mill for rolling material, such as a steel strip, the strip passes through several stands of the mill. The entry of the strip into the roll bite of the stand causes an impact load torque to be applied to the drive motors of the work rolls which are pulling the strip through the roll bite. When this load is applied to the speed regulator system, the drive speed suddenly drops. Any drop in drive speed of the stand which is being threaded will cause the strip to gather or buckle between the stand being threaded and the previous stand from which the strip has exited. The increase in strip storage will result in reduction or loss in the tension in the strip between the two stands in which the strip is being threaded. This loss in interstand tension in the strip is a serious operational problem for the mill, forcing the mill operator to manually operate the controls to change the drive speed of the stand or stands for the threading operation.
This manual operation of the controls sometimes results in an excessive increase in the drive speed and thus, an excessive removal of strip storage between the stands, resulting in strip breakage.
It is not only important that the drive speed of the stand in which the strip is being threaded speed recover as fast as possible, but also to overshoot a safe amount to quickly remove the strip storage between the stands caused by the speed drop due to the load impact to the drive motor without causing breakage to the strip.
Previous attempts may have been made to compensate for this impact load disturbance applied to a speed regulator drive system of a mill resulting in a speed drop of the drive motor. However, none of these systems have achieved this compensation in the same manner and with the same efficiency provided by the present invention.
The present invention uses an impact load controller which operates on the rate of change in speed error to first cause the stand speed to overshoot within safe limits and then to quickly bring this overshoot speed down to the threading speed or reference speed setting of the mill.